Hydraulic fracturing is a common stimulation technique used to enhance production of fluids from subterranean formations in, for example, oil, gas, coal bed methane and geothermal wells. In a typical hydraulic fracturing treatment operation, a viscosified fracturing fluid is pumped at high pressures and high rates into a wellbore penetrating a subterranean formation to initiate and propagate a hydraulic fracture in the formation. Subsequent stages of viscosified fracturing fluid containing particulate matter known as proppant, e.g., graded sand, ceramic particles, bauxite, or resin coated sand, are then typically pumped into the created fracture. The proppant becomes deposited into the fractures, forming a permeable proppant pack. Once the treatment is completed, the fracture closes onto the proppant pack, which maintains the fracture and provides a fluid pathway for hydrocarbons and/or other formation fluids to flow into the wellbore.
The fracturing fluid is usually a water-based fluid containing a gelling agent, e.g., a polymeric material that absorbs water and forms a gel as it undergoes hydration. The gelling agent serves to increase the viscosity of the fracturing fluid. The increased viscosity provides a number of advantages, including, among other things, improving the fracture propagating ability of the fluid and enabling the fracturing fluid to suspend and carry effective amounts of proppant.
While polymers have been used in the past as gelling agents in fracturing fluids, such polymers often tend to leave a coating on the proppant even after the gelled fluid is broken. The coating can interfere with the functioning of the proppant. Studies have also shown that “fish-eyes”and/or “microgels” present in some polymer gelled carrier fluids will plug pore throats, leading to impaired leakoff and potentially causing formation damage. Conventional polymers are also generally either cationic or anionic, which can also potentially damage the formation.
Aqueous fracturing fluids gelled with viscoelastic surfactants (VES) are also known in the art. VES-gelled fluids have been widely used as fracturing fluids because they exhibit excellent rheological properties and are less damaging to producing formations than crosslinked polymer fluids. VES fluids are non-cake-building fluids, and thus leave little or no potentially damaging polymer cake residue. However, the same property that makes VES fluids less damaging tends to result in significantly higher fluid leakage into the reservoir matrix, which can reduce the efficiency of the fluid, especially during VES fracturing treatments.
Another fluid known as a gravel packing fluid having relatively large grained sand, e.g., gravel, suspended therein also may be utilized to prevent migration of smaller grained sand from the subterranean formation into the well bore and to maintain the integrity of the formation. In particular, a permeable screen may be placed against the face of the subterranean formation, followed by pumping the gravel packing fluid into the annulus of the well bore such that gravel becomes packed against the exterior of the screen.
While advances have been made in well servicing fluids, further improvements in well servicing fluids would be a welcome addition in the field.